In recent years, developments of storage and supply systems of clean energy by solar photovoltaic power generation or wind power generation and new power source systems such as power sources used in electric vehicles and hybrid electric vehicles have been vigorously conducted. Although a lead battery, a nickel-cadmium battery and the like have heretofore been widely used as storage batteries in such new power source systems, that having a high energy density and a high power density has come to be required as a power source taking the place of these batteries.
Attention is paid to a lithium-ion battery and an electric double layer capacitor as storage power sources or driving power sources meeting such a requirement. However, the lithium-ion battery involves a problem in points of power characteristics, cycle life and safety though the energy density thereof is high.
On the other hand, since the electric double layer capacitor is excellent in power characteristics and has a long life withstanding charge and discharge over tens of thousands of cycles though the discharge capacity thereof is small compared with the battery, it is widely used as a power source for memory backup in portable telephones, digital cameras and the like. However, the energy density of a general electric double layer capacitor is of the order of 3 to 5 Wh/l and small by about two figures compared with the lithium-ion battery. Therefore, its practical use as a driving power source for hybrid electric vehicles or the like, of which an energy density of at least 10 to 20 Wh/l is required, is not developed under the circumstances.
As a storage power source meeting uses, of which a high energy density and high power characteristics are required, there has recently been proposed, as an organic electrolyte storage battery accompanied by transfer of lithium ions, an organic electrolyte capacitor using a positive-electrode current collector and a negative-electrode current collector each having holes penetrating therethrough from the front surface to the back surface, and a negative-electrode active material capable of reversibly carrying lithium, wherein a negative electrode is electrochemically brought into contact with lithium arranged oppositely to the negative electrode, thereby carrying the lithium on the negative-electrode active material (see Patent Arts. 1 and 2).    Patent Art. 1: International Publication No. WO/2003/003395, pamphlet    Patent Art. 2: International Publication No. WO/2005/031773, pamphlet
In such an organic electrolyte capacitor, the holes penetrating therethrough from the front surface to the back surface are provided in the current collector, whereby the lithium ions can be transferred between the front and back surfaces of the electrode without being intercepted by the electrode current collector. Therefore, in a cell structure having many stacked layers, the lithium ions can be electrochemically carried on not only a negative electrode arranged in the vicinity of the lithium, but also a negative electrode arranged away from the lithium through the through-holes.
As the current collector used in this organic electrolyte capacitor, is mentioned a porous metal foil having holes penetrating therethrough from the front surface to the back surface, for example, an expanded metal, a punching metal, a metal mesh, a foam or a porous etched foil with through-holes imparted by etching.
From the viewpoints of electrochemical characteristics and weight saving, it is investigated to use, as a positive-electrode current collector, an expanded metal, punching metal, electrolytically etched foil, chemically etched foil or the like worked from an aluminum base material, and on one hand, it is investigated to use, as a negative-electrode current collector, an expanded metal, punching metal, electrolytically etched foil, chemically etched foil or the like worked from a base material such as stainless steel, copper or nickel.